Fatty alcohol derivatives, particularly sulfates and ether sulfates, are versatile surfactants. They are used across a broad array of industries and end uses, including personal care, laundry and cleaning, emulsion polymerization, agricultural uses, oilfield applications, industrial compositions, and specialty foamers.
Fatty alcohols are usually made by reducing the corresponding fatty acids or esters, typically by catalytic hydrogenation. Often, the catalyst includes zinc or copper and chromium. U.S. Pat. No. 5,672,781, for instance, uses a CuCrO4 catalyst to hydrogenate methyl esters from palm kernel oil, which has substantial unsaturation, to produce a mixture of fatty alcohols comprising about 52 wt. % of oleyl alcohol, a monounsaturated fatty alcohol. For additional examples, see U.S. Pat. Nos. 2,865,968; 3,193,586; 4,804,790; 6,683,224; and 7,169,959.
The fatty acids or esters used to make fatty alcohols and their derivatives are usually made by hydrolysis or transesterification of triglycerides, which are typically animal or vegetable fats. Consequently, the fatty portion of the acid or ester will typically have 6-22 carbons with a mixture of saturated and internally unsaturated chains. Depending on source, the fatty acid or ester often has a preponderance of C16 to C22 component. For instance, methanolysis of soybean oil provides the saturated methyl esters of palmitic (C16) and stearic (C18) acids and the unsaturated methyl esters of oleic (C18 mono-unsaturated), linoleic (C18 di-unsaturated), and α-linolenic (C18 tri-unsaturated) acids. The unsaturation in these acids has either exclusively or predominantly cis-configuration.
Recent improvements in metathesis catalysts (see J. C. Mol, Green Chem. 4 (2002) 5) provide an opportunity to generate reduced chain length, monounsaturated feedstocks, which are valuable for making detergents and surfactants, from C16 to C22-rich natural oils such as soybean oil or palm oil. Soybean oil and palm oil can be more economical than, for example, coconut oil, which is a traditional starting material for making detergents. Metathesis relies on conversion of olefins into new products by rupture and reformation of carbon-carbon double bonds mediated by transition metal carbene complexes. Self-metathesis of an unsaturated fatty ester can provide an equilibrium mixture of starting material, an internally unsaturated hydrocarbon, and an unsaturated diester. For instance, methyl oleate (methyl cis-9-octadecenoate) is partially converted to 9-octadecene and dimethyl 9-octadecene-1,18-dioate, with both products consisting predominantly of the trans-isomer. Metathesis effectively isomerizes the cis-double bond of methyl oleate to give an equilibrium mixture of cis- and trans-isomers in both the “unconverted” starting material and the metathesis products, with the trans-isomers predominating.
Cross-metathesis of unsaturated fatty esters with olefins generates new olefins and new unsaturated esters that can have reduced chain length and that may be difficult to make otherwise. For instance, cross-metathesis of methyl oleate and 3-hexene provides 3-dodecene and methyl 9-dodecenoate (see also U.S. Pat. No. 4,545,941). Terminal olefins are particularly desirable synthetic targets, and Elevance Renewable Sciences, Inc. recently described an improved way to prepare them by cross-metathesis of an internal olefin and an α-olefin in the presence of a ruthenium alkylidene catalyst (see U.S. Pat. Appl. Publ. No. 2010/0145086). A variety of cross-metathesis reactions involving an α-olefin and an unsaturated fatty ester (as the internal olefin source) are described. Thus, for example, reaction of soybean oil with propylene followed by hydrolysis gives, among other things, 1-decene, 2-undecenes, 9-decenoic acid, and 9-undecenoic acid. Despite the availability (from cross-metathesis of natural oils and olefins) of unsaturated fatty esters having reduced chain length and/or predominantly trans-configuration of the unsaturation, sulfated and sulfonated derivatives of the unsaturated fatty alcohols appear to be unknown.
In sum, traditional sources of fatty acids and esters used for making unsaturated fatty alcohols and their sulfate and ether sulfate derivatives generally have predominantly (or exclusively) cis-isomers and lack relatively short-chain (e.g., C10 or C12) unsaturated fatty portions. Metathesis chemistry provides an opportunity to generate precursors having shorter chains and mostly trans-isomers, which could impart improved performance when the precursors are converted to downstream compositions (e.g., in surfactants).
Sulfation of alcohols produces alcohol sulfates, which have an C—O—SO3X group, where X is typically an alkali metal or ammonium ion from a subsequent neutralization step. Sulfonation of unsaturated hydrocarbons gives sulfonates, which have a C—SO3X group. When an unsaturated alcohol is the starting material, the unsaturated sulfate can be produced under some conditions (see, e.g., WO91/13057). With other reagents, alcohol sulfation and carbon-carbon double bond sulfonation may compete, with most of the reaction product resulting from sulfation, although the nature of the sulfonated by-products is generally not well understood (see, e.g., U.S. Pat. No. 5,446,188). Because of the competing side reactions, unsaturated alcohols are usually avoided when the goal is to make an alcohol sulfate or ether sulfate.